Overload relief system for power presses



Dec. 8, 1964 L. s. PLATOU OVERLOAD RELIEF SYSTEM FOR POWER PRESSES 4 Sheets-Sheet 1 Filed April 9, 1964 ENTOR. Law 5. PLA TOU BY /@W BMW ATTO/Z NEYS Dec. 8, 1964 L. s. PLATOU 3,160,089

OVERLOAD RELIEF SYSTEM FOR POWER PRESSES Filed April 9, 1964 4 Sheets-Sheet 2 /e 25 H F26. 2.

I INVENTOR. l3 Levy 5. PLATOU A'TTORNE KS Dec. 8, 1964 s. PLATOU OVERLOAD RELIEF SYSTEM FOR POWER PRESSES 4 Sheets-Sheet 3 Filed April 9, 1964 INVENTOR. A E/ 1/ 5. PLA TOU BY fiww ATTORNEYS Dec. 8, 1964 s. PLATOU OVERLOAD RELIEF SYSTEM FOR POWER PRESSES 4 Sheets-Sheet 4 Filed April 9, 1964 0 m0 T7 WA vL p N E A TTOIQNEVS United States Patent 3,160,089 @VERLQAD RELKEF SYSTEM FQR PQWER PRESES Leiv S. Piston, Snyder, NAG, assiguor to Niagara Machine & Tool Works, Enfialo, Filed Apr. 9, 1964, Ser. No. 358,474 12 Claims, (ill. filth-21d) This invention relates to power presses and similar reciprocating machines which are subjected to severe temporary stresses and strains and the invention relates particularly to overload release means for such presses or similar machines.

In the power press and related arts it is well known to interpose hydraulic means in one or more of the structural members of the machine which are apt to be subjected to extreme or undue loading, the hydraulic means comprising generally a piston and cylinder arrangement with the piston fixes to one portion of the structure and the cylinder to another in such manner that stress in the structure applies force to the piston and cylinder means so that internal fluid pressure is developed in proportion to the stress or strain in the machine structure.

in these prior art piston and cylinder or other hydraulic overload arrangements pressure limiting valves or similar devices are usually employed which release when the fluid pressure reaches a predetermined magnitude. This release permits relative movement between the piston and cylinder, for instance, and thus interrupts the normal rigidity of the structure in which the hydraulic means is interposed, thus permitting relative movement which relieves the strain due to overload or the like.

By way of example, the vertical tie rods of power presses are commonly subjected to tensile forces proportionate to the loading of the press. It has been proposed to fix power press tie rods to the press structure at one end and provide piston members at their other ends. These piston members act in hydraulic cylinders which are fixed to the press structure at such other ends of the tie rods. When the cylinder is hydraulically blocked the piston is in effect locked therein and the tie rods serve their normal functions as tensile members in the power press framework.

However, under overload, abnormal fluid pressure in the cylinders opens a fluid pressure responsive valve whereupon fluid may flown from the cylinder. This has the ef fect of permitting the tie rod to increase its effective length, thus eliminating the overload. Similiar hydraulic overload arrangements may be incorporated'in members of the press structure which are subjected to compression under load, as for instance the connecting rods or connections between a crankshaft or eccentric shaft ofa power press and the work perform ng ram or slide.

' The foregoing hydraulic overload arrangements are not entirely satisfactory since, generally speaking, release under overload cannot normally take place until substantial deflection under overload has taken place, since opening movement of pressure sensitive hydraulic pressure limiting valves normally presupposes substantial relative physical movement of the valve parts under excess hydraulic pressure thereagainst.

The hydraulic overload release arrangement of the present invention is highly novel and useful and differs substantially from prior art arrangements for this general purpose in that the hydraulic fluid release is not triggered or initiated by the development of excess hydraulic pressure, as such, in the overload device or devices. In the present invention extraneous strain-sensitive means such as the well-known electrical strain gages are applied to parts which are subjected to or reflect the degree of strain in proportion to loading of the machine.

The indications of such strain gages, when excessive ice in magnitude, actuate valves which permit hydraulic fluid flow to or from hydraulic overload relief devices which may be otherwise similar to those of the prior art. Thus the sensitivity of the overload release is not controlled or limited by the normal and usual force differential required to cause operation of a pressure relief valve or the like.

Furthermore, in the arrangement of the present invention the strain gages or similar stress-measuring devices may be located precisely at critical strain points, whether such critical points he on frame portions of the press or on movable parts such as the connections'between the crankshaft or eccentric shaft of a press and the like or ram which is reciprocated thereby. Also, the strain gages need not coincide in number with the hydraulic overload release devices. For instance, there may be strain gages on two connections or connecting rods and overload release devices on four tie rods.

In accordance with the present invention the strain measurements of the several strain gages are averaged and the net effect is applied equally and uniformly to the several overload release devices. Adjustment and control of the degree of overload and restoration of the apparatus following correction or elimination of an overload condition is also greatly facilitated by the system of the present invention.

A single specific embodiment of the principles of the present invention is illustrated in the accompanying drawings and described in the following specification. However, it is to be understood that such embodiment is by way of example only and that various mechanical, electrical and hydraulic modifications may be made therein without departing from the spirit or scope of the invention, the same being limited only as defined in the appended claims.

In the drawings:

FIG. 1 is a general front elevational view of a power press equipped with one form of the overload release arrangement of the present invention;

PEG. 2 is a top plan view of the structure of FIG. 1; FIG. 3 is a fragmentary side elevational view of the structure of FIG. 1;

FIG. 4 is an enlarged cross sectional view of the upper end of one of the tie rods'of the power press of FIGS. 1 through 3 showing one form of the hydraulic piston and cylinder overload release arrangement of the present invention associated therewith; and

FIG. 5 is a schematic drawing of the hydraulic circuitry of the form of the invention shown in FIGS. 1 through 4.

Like characters of reference denote like parts throughout the several figures of the drawings. Referring first particularly to FIG. 1, the power press there illustrated is generally conventional in form, comprising a die-receiving bed 163, side columns 11 and 12, a crown l3, and a vertically reciprocable slide or ram 14. The structural frame of the press, comprising the bed, the side columns and the crown, is retained and held in assembled relationship by four tie rods 16 which extend vertically at the four corners of the press as appears best in FIG. 2'.

The lower ends of the tie rods 16 are equipped with nuts 17 which engage against the lower side of bed It in the usual manner. The upper ends of the tie rods are providedwith means which bear against the upper end of crownlfi, such means being illustrated in cross sectional detail in FIG. 4. In the present instance the power press is of the type driven from eccentric shafts, the shafts being designated 2t? in FIG. 1, and connections or connecting rods Zlextend from the eccentric formations of the shafts 2% to the slide 14 to reciprocate the latter.

As is well known, power pressing operations engender large forces tending to force the bed and crown apart in a vertical direction,which forces result in tensile stresses in the tie rods 16. Corresponding compressive forces are developed in the connections 21. While the principles of the present invention may be variously adapted, it may be assumed that in the present instance there are two. eccentries on each shaft and fore and aft connections 21 from each eccentric to the slide 14.

Reference will now be had to the hydraulic means pro vided at the upper end of each tie rod 16 through which the tie rod normally exerts a retaining force against the upper end of crown 13. In the system of the present invention this force is relieved in a novel manner under overload conditions, as will presently appear. As stated in the preamble hereto, the use of hydraulic force means for tie rod engagement is known in this art and the principalnovelty of the present invention resides in the manner in which overload conditions are measured and the manner in which this measurement is employed to relieve the overload condition through the instrumentality of the hydraulic means.

Referring to FIG. 4, the upper end of each tie rod 16 is threaded in the usual manner as at 24 to receive the usual nut 25. Instead of bearing directly downwardly against the crown 13 in the conventional manner, each nut 25 bears downwardly against an annular piston member 26 which is received in the upper end of a cylinder member 27. Fluid seal members in the form of Q-rings or the like are provided'as between the piston 26 and cylinder 27, piston 26 and tie rod 16, and the cylinder 27 and tie rod 15, all as indicated at 28, 29. and 30, respectively.

It will be noted that the restraining force of each tie rod 16 will be proportionate to the degree of hydraulic pressure within its cylinder member 27 beneath piston 26. A predetermined degree of hydraulic pressure is normally maintained in cylinder 27 through a passage 31 and cooperating fluid pressure means which will be described later herein in a description of the hydraulic circuitry illustrated in FIG. 5. An unloadingvalve for each cylinder 27 is designated generally by the reference numeral 32. Each unloading valve 32 comprises a generally cylindrical upright body member 33 which is attached to its associated cylinder member 27 by a nipple 34-which establishes fluid communication between the space within cylinder member 27 and the interior of unloading valve 32.

The valve body member 33 is bored at its upper end to receive a generally cylindrical valve member 35 which seats downwardly against annular valvesea-t 36. A discharge passage 37 leads downwardly through valve seat 36. A cap 38 threads into the upper end of body member 33 and is bored as at 39 to receive an upper reduced portion 400i valve member 35. A compression coil spring 41 seats in a bore in the upper end of valve member 35 and engages against the under side of cap 38 to urge valve member 35 downwardly against seat 36. A passage 42 in cap 38 merely vents the interior of cap 38.

It will be noted that the reduced portion 4 3 of valve member 35 forms an annular fluid chamber 45 above the main cylindrical body portion of valve 35. As shown in FIG. 4, the fluid pressure passage which connects between the interior of cylinder 27 and the lower portion of valve body member 33 through nipple 34 is designated 46 in FIG. 4 and communication between such passage 46 and annular chamber 45 is established by way of a passage 47 in body member 33. Passage 47 is adjustably restricted by a needle valve 48 so that pressure in chamber 45 will normally equalize with respect to pressure in cylinder 27 and passage 46 if given suificient time.

v A fluid passage 50 leads from annular fluid passage 45 and passage 50 is normally blocked. Upon excessive loading, means are provided for unblocking passage 51 so that fluid may flow freely therefrom. This operation will be more fully described in conjunction with the hydraulic circuit diagram (FIG. j

It will be noted that the lower portion of annular fluid chamber 45 is defined by an annular ledge 51 at the upper end of the main cylindrical body portion of valve 35 and that an opposing annular ledge of less area than ledge 51 is provided at the bottom of the main body portion of valve 35, such lower ledge being designated 52.

Thus when passage 50 is blocked and fluid pressures in chamber 45 and passage 46 are equal, the greater area of ledge 51 will cause valve to be held seated by such fluid pressure. However, if passage 50 is unblocked, the pressure in chamber will rapidly fall due to the restricted fluid flow past needle valve 48 and the fluid pressure against the bottom ledge 52 of valve 35 will accordingly cause the valve to lift and fluid pressure from the interior of cylinder 27 will discharge through passage 46 and through the discharge passage 37 of valve 32.

From the foregoing it will be seen that release of hydraulic fluid through the unblocking passage results in opening of valve 35 and consequent dumping of hydraulic fluid from beneath piston 26 in cylinder 27 through discharge passage 37. This has the effect of relieving the downward force normally exerted on crown 13 by the tie rods through the medium of the nuts 25, pistons and cylinders 26 and the hydraulic pressure fluid column normally present beneath piston 26.

Reference will now be had to FIG. 5 which shows hydraulic circuitry for jointly controlling the hydraulic piston and cylinder members 26 and 27 of the four tie rods 7 of a power press so that all four tie rods release in the foregoing manner when an electrical signal which is developed extraneously of the piston and cylinder means indicates an overload condition. 5

In FIG. 1 the numeral 55 indicates strain gages applied to the connections 21 of the power press, which strain gages indicate electrically the degree of strain, in this case compressive, developed during working operation of the press. The manner in which the indications of the several strain gauges 55 are correlated and averaged to produce a composite load indicating electrical signal is not novel to the present application.

However, further reference will be made to the electrical strain gage indication translating means later herein. For an understanding of the hydraulic circuitry of FIG. 5 it is sufiicient to state that an electric overload signal of a predetermined degree energizes the operating solenoid of a normally closed two-way solenoid valve designated 57 in FIG. 5.

The normal preloading hydraulic pressure which is applied to each cylinder 27 by way of passage 31 thereto for maintaining correct tie rod tension is supplied to the several passages 31 by a pressure manifold 58 which derives hydraulic fluid pressure from an air driven hydraulic pump 59. Liquid flow from pump 59 to manifold 58' is by way of a conduit 60 wlnch contains a filter 61, a pressure gauge 62 and a differential pressure regulator valve 63 which maintains tie rod tensioning fluid pressure in the cylinders 27 within a predetermined range, for instance, 4800 to 5000 pounds per square inch in a typical instance.

Operating air for the air driven hydraulic pump is supplied by way of an air line 66 which may contain a manual shut-off valve 67, a filter 68, a pressure regulator 69, a lubricator 70 and a two-way solenoid air valve 71 which may be under common control with the main drive motor of the press so that pump 59 is inoperation whenever the press drive motor is running. The several branch passages 31 from pressure manifold 58 contain check valves 72 which prevent retrograde flow of hydraulic pressure fluid from cylinders 27 through passages 31. The several unblocking passages 53 of the blocking valves 32 lead to a manifold 75 which is controlled 'by the aforesaid solenoid valve 57 and, by way of a conduit 77, leads back to a reservoir 7 6 from which'hydraulic liquid for the circuit is drawn by pump 59.

and the consequent raising of the valve members 35 causes' liquid to dump from cylinders 27 through discharge passages 37 as described earlier herein and the several discharge passages 37 communicate with a manifold 7 8 which leads freely back to reservoir 76.

The load indicator and the limit control signal which actuates the solenoid valve 57 when a predetermined overload occurs may be as illustrated and described in detail in the pending patent application of Robert E. Vosteen and Clarence 0. Jones, In, Serial No. 151,851, filed November 13, 1961. In this indicator and control circuitry the outputs of a plurality of variously located strain gauges are accumulated and analyzed and the resultant signal provides a visual reading and also provides a machine stopping electrical signal which is used in the present combination to control the solenoid of valve 57.

Other examples of electric circuitry suitable for acting under the joint control of a plurality of strain gages for producing a resultant machine controlling electrical signal for use in measuring press loading are available in the prior art, for instance, Colten et al. Patent No. 2,924,968, dated February 16, 1960, and therefore the electrical circuitry acting between the strain gages 55 and the solenoid of valve 57 need not be set forth herein. A control console of the electrical apparatus of the above Vosteen et al. patent application is indicated at 80 in FIG. 1.

I claim:

1. In a power press subject to varying stress incident to working strokes thereof, frame means, a hydraulic piston and cylinder each engaging a portion of said frame means whereby said stress produces a force tending'to move said piston relative to said cylinder, means for maintaining a hydraulic pressure in said-cylinder normally preventing such movement, an electrical strain gage applied to a stress member of said press and adapted to put forth an electrical signal proportionate to stress in said member, a fluid discharge passage from said cylinder and a valve therein normally closed against fluid egress from said cylinder, and solenoid means operable to open said valve when said strain gage signal exceeds a predetermined magnitude.

2. in a power press subject to varying stress incident to working strokes thereof, frame means, a hydraulic PIS- ton and cylinder each engaging a portion of said frame means whereby said stress produces a force tending to move said piston relative to said cylinder, means for maintaining a hydraulic pressure in said cylinder normally preventing such movement, transducer means comprising a plurality of electrical strain gages applied to stress members of said press and adapted to put forth electrical signals proportionate to stress in said members, and means integrating said signals to produce a resultant signal, a fluid discharge passage from said cylinder and a valve therein normally closed against fluid egress from said cylinder, and solenoid means operable to open said valve when said strain gage resultant signal exceeds a predetermined magnitude.

3. In a power press, a plurality of vertical tie members connecting upper and lower portions of said press, a hydraulic piston and cylinder mechanism associated with each of said tie members whereby stress in said tie members incident to working strokes of said press produces forces tending to move said pistons relative to said cylinders, means for maintaining hydraulic pressure in said cylinders normally preventing such movement, an elecrical strain gage applied to a stress member of said press and adapted to put forth an electrical signal proportionate to stress in said member, fluid discharge passages from said cylinders, and valves therein normally closed against fluid egress from said cylinders, and solenoid means operable to open said valves when said strain gage signal exceeds a predetermined magnitude.

4. In a power press, a plurality of vertical tie members connecting upper and lower portions of said press, a bydraulic piston and cylinder mechanism associated with each of said tie members whereby stress in said tie mem-' bers incident to working strokes of said press produces forces tending to move said pistons relative to said cylinders, means for maintaining hydraulic pressure in said cylinders normally preventing such movement, transducer means comprising a plurality of electrical strain gages applied to stress members of said press adapted to put forth electrical signals proportionate to stresses in said members and means integrating said signals to produce a resultant signal, fluid discharge passage from said cylinders and valves normally closed against fluid egress from said cylinders, and solenoid means operable to open said valves when said resultant signal exceeds a predetel-mined magnitude.

5. in a reciprocating machine, a plurality of tie members connecting end portions of said machine, a hydraulic piston and cylinder mechanism associated with each of said tie members whereby stress in said tie members incident to working strokes of said machine produces forces tending to move said pistons relative to said cylinders, said cylinders containing hydraulic fluid normally preventing such movement, strain sensing means applied to a stress member of said machine and adapted to supply a signal proportionate to stress in said member, fluid discharge passages from said cylinders and valves therein normally closed against fluid egress from said cylinders, and means operable to open said valves when said signal exceeds a predetermined magnitude.

6. In a reciprocating machine, a plurality of tie members connecting end portions of said machine, a hydraulic piston and cylinder mechanism associated with each of said tie members whereby stress in said tie members incident to working strokes of said machine produces forces tending to move said pistons relative to said cylinders, said cylinders containing hydraulic fluid normally preventing such movement, strain sensing means applied to stress members of said machine and adapted to supply signals proportionate to stresses in said members, means integrating said signals to produce a resultant signal, fluid discharge passages from said cylinders and valves therein normally closed against fluid egress from said cylinders, and means operable to open said valves when said resultant signal exceeds a predetermined magnitude.

7. In a reciprocating machine subject to varying stresses incident to working strokes thereof, frame means, a hydraulic piston and cylinder each engaging a portion of said frame means whereby said stresses produce forces tending to move said piston relative to said cylinder, said cylinder containing hydraulic fluid normally preventing such movement, strain sensing means applied to a stress member of said machine and adapted to supply a signal proportionate to stress in said member, a fluid discharge passage from said cylinder and a valve therein normally closed against fluid egress from said cylinder, and means operable to open said valve when said signal exceeds a predetermined magnitude.

8. In a reciprocating machine subject to varying stresses incident to working strokes thereof, frame means, a hydraulic piston and cylinder each engaging a portion of said frame means whereby said stresses produce forces tending to move said piston relative to said cylinder, said cylinder containing hydraulic fluid normally preventing such movement, strain sensing means applied to stress members of said machine and adapted to supply signals proportionate to stresses in said members, means integrating said signals to produce a resultant signal, a fluid discharge passage from said cylinder and a valve therein normally closed against fluid egress from said cylinder, and means operable to open said valve when said resultant signal exceeds a predetermined magnitude.

9. In a reciprocating machine subject to varying stress incident to working strokes thereof, frame means, hydraulic means acting between portions of said frame means whereby stress in said frame means produces a force acting against said hydraulic means, an electrical strain gage applied to a stress member of said machine and adapted to put forth an electrical signal proportionate to stress in said member, a fluid discharge passage from said hydraulic means and a valve therein normally closed against fluid egress from said hydraulic means whereby said hydraulic means normally prevents relative movement between said portions of said frame means, and solenoid means operable to open said valve when said strain gage signal exceeds a predetermined magnitude to free said frame means portions for relative movement to relieve overload thereof.

10. In a reciprocating machine subject to varying stress incident to working strokes thereof, frame means, hydraulic means acting between portions of said frame means whereby stress in said frame means produces a force acting against said hydraulic means, transducer means comprising a plurality of electrical strain gages applied to stress members of said machine and adapted to put forth electrical signals proportionate to stresses in said members and means integrating said signals to produce a resultant signal, a fluid discharge passage from said hydraulic means and a valve therein normally closed against fluid egress from said hydraulic means whereby said hydraulic means normally prevents relative movement between said portions of said frame means, and

solenoid means operable to open said valve when said.

resultant signal exceeds a predetermined magnitude to free said frame means portions for relative movement to relieve overload thereof.

11. In a reciprocating machine subject to varying stress incident to working strokes thereof, frame means, hydraulic means acting between portions of said frame means whereby stress in said frame means produces a force acting against said hydraulic means, strain sensing means applied to a stress member of said machine and adapted to supply a signal proportionate to stress in said member, a fluid discharge passage from said hydraulic means and a valve therein normally closed against fluid egress from said hydraulic means whereby said hydraulic means normally prevents relative movement between said portions of said frame means, and solenoid means operable to open said valve when said signal exceeds a predetermined magnitude to free said frame means portions for relative movement to relieve overload thereof.

12. In a reciprocating machine subject to varying stress incident to working strokes thereof, frame means, hydraulic means acting between portions of said frame means whereby stress in said frame means produces a force acting against said hydraulic means, strain sensing means applied to stress members of said machine and adapted to supply signals proportionate to stresses in said members, means integrating said signals to produce a resultant signal, a fluid discharge passage from said hydraulic means and a valve therein normally closed against fluid egress from said hydraulic means whereby said hydraulic means normally prevents relative movement beween said portions of said frame means, and solenoid means operable to open said valve when said resultant signal exceeds a predetermined magnitude to free said frame means portions for relative movement to relieve overload thereof.

References flirted by the Examiner UNITED STATES PATENTS 1,872,115 8/32 Byerlein 100-282 X 2,522,450 9/50 Johansen 192-150 X 2,616,543 11/52 Danly 100-53 X 2,770,342 11/56 Johansen 192-150 2,937,733 5/60 Danly 192-150 FOREIGN PATENTS 581,753 8/33 Germany.

WALTER A. SCHEEL, Primary Examiner. 

1. IN A POWER PRESS SUBJECT TO VARYING STRESS INCIDENT TO WORKING STROKES THEREOF, FRAME MEANS, A HYDRAULIC PISTON AND CYLINDER EACH ENGAGING A PORTION OF SAID FRAME MEANS WHEREBY SAID STRESS PRODUCES A FORCE TENDING TO MOVE SAID PISTON RELATIVE TO SAID CYLINDER, MEANS FOR MAINTAINING A HYDRAULIC PRESSURE IN SAID CYLINDER NORMALLY PREVENTING SUCH MOVEMENT, AN ELECTRICAL STRAIN GAGE APPLIED TO A STRESS MEMBER OF SAID PRESS AND ADAPTED TO PUT FORTH AN ELECTRICAL SIGNAL PROPORTIONATE TO STRESS IN SAID MEMBER, A FLUID DISCHARGE PASSAGE FROM SAID CYLINDER AND A VALVE THEREIN NORMALLY CLOSED AGAINST FLUID EGRESS FROM SAID CYLINDER, AND SOLENOID MEANS OPERABLE TO OPEN SAID VALVE WHEN SAID STRAIN GAGE SIGNAL EXCEEDS A PREDETERMINED MAGNITUDE. 